1. Field of the Invention
The present invention relates to a method and an apparatus used for plasma treatment of substrate materials such as semiconductor substrates or wafers. The plasma treatment includes chemical vapor deposition by means of plasma, for example, the deposition of insulating substances or semiconductor substances on the surfaces of the semiconductor materials, and plasma etching, for example, the etching of semiconductor materials or of the coatings formed on the semiconductor materials.
2. Description of the Prior Art
A proposal was made in U.S. Pat. No. 3,837,856, in which a first chamber containing semiconductor wafers is located at a predetermined distance from a second chamber which produces a plasma discharge, this second chamber being communicated with the first chamber through the connection path at an end of the second chamber. Reaction substances in an plasma produced by the electrodeless radio frequency excitation in the second chamber are transmitted to the first chamber through the connection path. Semiconductor materials are treated by such reaction substances in the first chamber. However, according to this U.S. Patent, a uniform distribution of the plasma treatment cannot be realized either with regard to the surface of a semiconductor wafer or with regard to a series of semiconductor wafers, the speed of the plasma treatment cannot be increased because of a decrease in the effectiveness of the reaction substances and because of a loss of the reaction substances due to their being deposited on the walls of the first and the second chambers, and the speed of mass-producing the treated semiconductor materials in relatively low because of the limited number of semiconductor wafers which are treated simultaneously in the first chamber. Besides, if this U.S. Patent is used for carrying out chemical vapor deposition of semiconductor materials, undesirable vapor decomposition tends to take place, and the impurities produced by such decomposition are included in the deposit, which forms the coating on the semiconductor material, so that the quality of the coating becomes poor.
Another plasma treatment was proposed in U.S. Pat. No. 3,615,956, in which semiconductor wafers are placed into a number of parallel slots extending longitudinally in a boat arranged in the reaction tube. A pair of elongated semicircular plates is provided on the outer surface of the reaction tube. The surfaces of the semiconductor wafers are all arranged in parallel with the axis of the reaction tube. However, according to this U.S. Patent, the effects of the plasma treatment are not uniform with regard to the position of the semiconductor wafer in the reaction tube, the speed of the plasma treatment cannot be easily increased and the diameter of the cross-section of the reaction tube tends to become too large if the number of the rows of semiconductor wafers is increased.
Another proposed plasma treatment method is known to manufacturers of semiconductor devices in which a batch of semiconductor wafers is treated on a plate arranged in a bell-jar type treatment vessel, instead of being arranged in tubular treatment vessels which have horizontal axes, as disclosed in the above-mentioned U.S. patents. A group of semiconductor wafers (i.e., the first batch) is placed flat on the plate in the treatment vessel during the plasma treatment, then these wafers are replaced by another group of semiconductor wafers (i.e., the next batch). However, the speed of mass-producing the treated semiconductor wafers cannot be easily increased because of the limited number of semiconductor wafers which can be included in a batch.
The present invention originated from attempts to solve the above-mentioned problems in the prior art.